It's not obvious at first glance, but serene Pinto Lake is full of toxic algae blooms, and on Monday, officials who gathered there said it may be the most toxic lake in the state.

State Senator Bill Monning and Assemblyman Luis Alejo joined scientist and Santa Cruz County environmental health officials for a briefing on the lake's increasing toxicity.

Studies have shown that nitrogen and phosphorous deposited in the lake 100 years ago are the main culprits in causing the algae growth. More recently, storm runoff containing sewage and chemicals from nearby agricultural fields have also made the problem worse.

When temperatures rise during the late spring, summer and fall months, Pinto Lake experiences heavy blooms of blue green algae, also known as cyanobacteria.

High levels of phosphorous in the lake's sediments feed cyanobacteria, and the cyanobacteria create toxins.

Santa Cruz County water resources director John Ricker said toxins in the lake exceed safe swimming levels.

Signs are posted around the park warning that entering the 8,000-year-old lake, and having any direct contact with water, is dangerous.

So far, health officials said they feel lucky that no humans have become ill. The lake has killed sea otters, birds, dogs, and fish, including 200 carp that washed up dead in December.

Due to the complex nature of this problem, there is probably no quick fix solution.

Robert Ketley, a Watsonville water quality specialist, said recent studies have found some solutions, such as introducing alum, a chemical compound that would impede the release of phosphorous.